Characterization of the Flocculation Process from the Evolution of Particle Size Distributions
Publication: Journal of Environmental Engineering
Volume 134, Issue 5
Abstract
A flocculator-imaging system was developed to characterize the dynamics of particle size distribution (PSD) during flocculation. The system consisted of a flocculator coupled with an external flow-through cell for observation and photography, a microscopic charge-coupled device video recorder with backlighting, and an image analyzer. This nonintrusive side-stream setup was used to record the evolution of the PSD to determine the flocculation dynamics of three types of particle systems: Clean kaolin, kaolin coated with natural organic matter (NOM), and the kaolin/NOM system after ozonation. In addition to the PSD measurement, the potential, NOM reduction, and turbidity removal after the jar test of flocculation and sedimentation were determined for the particle systems at various alum dosages. The results of the -potential analysis and the PSD measurement indicated that flocculation takes place rapidly to form highly porous aggregates when the particle surface charge is fully neutralized. The adsorption of NOM on the particle surface stabilized the particles considerably, and thus hindered the flocculation process. Sweep flocculation using a much higher alum dosage was an effective means of process enhancement for the removal of particulates and associated organic matter. Ozonation of the kaolin/NOM solution, however, did not appear to have any positive effect on particle destabilization and flocculation. It is argued that ozonation produced more acidic functional groups in the NOM on kaolin, which increased the surface charge density and hence the stability of the particles in softer water.
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Acknowledgments
This research was supported by Grant Nos. UNSPECIFIEDHKU7120/03E and UNSPECIFIEDHKU7149/06E from the Research Grants Council (RGC) of the Hong Kong SAR Government and funding from the Outstanding Young Researcher Award to X.Y. Li from the University of Hong Kong. The writers are grateful to Dr. Edward Chian from the Georgia Institute of Technology, who provided the valuable NOM solution for the experimental study. The technical assistance of Mr. K. C. H. Wong is highly appreciated.
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Information & Authors
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Published In
Journal of Environmental Engineering
Volume 134 • Issue 5 • May 2008
Pages: 369 - 375
Copyright
© 2008 ASCE.
History
Received: Aug 11, 2005
Accepted: Oct 29, 2007
Published online: May 1, 2008
Published in print: May 2008
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